1. Field of the Invention
The present invention relates to an endoscope, or more particularly, to an endoscope characterized by a distal cover thereof that is freely detachable from a distal part of an insertion unit.
2. Description of the Related Art
In recent years, endoscopes having an elongated insertion unit have been widely adopted in the fields of medicine and industry. The distal part of the insertion unit is formed with a rigid distal member to which an illuminating means and viewing means are fixed.
When the rigid distal part is inserted into a tortuous body cavity in a human body, if the insertion unit is thrust too forcibly with the rigid distal part in contact with the bent part of the cavity wall, there arises a possibility of injuring the cavity wall with the rigid distal part.
In some endoscopes, a portion on the front side of the distal part is shielded with a distal cover having elasticity in order to prevent the distal part from injuring the cavity wall during insertion.
In another endoscope, a stowage in which a stand used to stand a therapeutic instrument is stowed so that the stand can pivot freely is formed with a distal cover. In particular, when the stand used to stand a therapeutic instrument is stowed, it is necessary to fully clean and sterilize the distal cover after use. The distal cover is therefore often structured to be freely detachable.
For example, in a prior art disclosed in Japanese Unexamined Patent Publication No. 8-19509, a cap similar to a distal cover is fixed to a main distal part by inserting a fixing screw into a screw hole in the main distal part, and then affixed thereto using a sealant. Furthermore, a screw hole larger than the screw hole in the main distal part is bored in the cap. For removing the cap, after the fixing screw is detached, a separation screw is used to push the main distal part in order to separate (detach) the cap affixed to the main distal part using the sealant.
However, in a structure like the structure of the prior art in which the distal cover (cap) is fixed using a screw, a jig such as a driver is needed to attach the distal cover. If the jig is missing, the distal cover cannot be attached. Moreover, the screw is inserted into the distal part and is therefore small in size. The screw is liable to get missing. If the screw gets missing prior to an endoscopic examination, the distal cover cannot be fixed and the examination cannot be started. Moreover, since the screw must be tightened to fix the distal cover, the work is cumbersome. Furthermore, the separation screw is needed to detach the cap.
By the way, a distal cover formed with an elastic member made of a rubber or the like and having a hole into which a convex part of a main distal part is fitted is conceivable as a simple detachable distal cover. This structure has possibilities of not being fixed satisfactorily, being positioned with poor precision, or being displaced or coming off during an examination.
Talking of a known side-looking endoscope, Japanese Unexamined Patent Publication No. 8-243071 has disclosed an endoscope in which a distal cover thereof is made detachable and the efficiency in cleaning the surroundings of a forceps stand is improved. In this endoscope, as shown in FIG. 51, the distal cover is thrust in an axial direction, a jut 503 of a distal part 502 is fitted into a hole 501 in a cover 500, and the cover is fixed using a screw 504. According to this method described in the Japanese Unexamined Patent Publication No. 8-243071, if the screw 504 comes off after the endoscope is inserted into a body cavity, there is no means for recognizing the fact. If the screw 504 comes off within the body cavity and the cover 500 almost comes off, the fact cannot be recognized until the cover 500 drops. This is a critical problem in terms of safety.
In medical-purpose endoscopes including a gastroscope and duodenoscope, an insertion unit of an endoscope is inserted into a patient's body cavity in order to view or treat a lesion. Some medical-purpose endoscopes include a therapeutic instrument standing unit as a mechanism for directing forceps or any other therapeutic instrument toward a desired lesion so as to collect a biomedical tissue or treat the lesion while viewing the lesion.
The therapeutic instrument standing unit basically comprises a therapeutic instrument stand capable of pivoting with a standing axis located in a distal structure as a center, and an operation wire coupled to the therapeutic instrument stand. When an operator advances or withdraws the operation wire by handling an operation unit, the angle of the therapeutic instrument stand is changed to direct the forceps in a desired direction.
When the endoscope is in operation, intracavitary fluid invades into an area in which the standing axis of the therapeutic stand and the distal structure are engaged with each other, or an area in which an operation wire fixing member connected to an end of the operation wire and the therapeutic instrument stand are engaged with each other.
The endoscope must therefore be cleaned (sterilized) after use. It is time-consuming to clean the operation wire fixing member and standing axis. Under the circumstances, Japanese Unexamined Patent Publication No. 7-323001 has proposed an endoscope whose distal cover is easily attachable or detachable to or from a distal structure.
However, in known endoscopes, in which a distal cover is freely detachable from a distal structure, including the endoscope disclosed in the Japanese Unexamined Patent Publication No. 7-323001, a small gap may be created between the distal cover and distal structure. In this state, if a treatment using a high-frequency current is carried out, there arises a possibility that the high-frequency current may leak out to the outer surface of a distal part via intracavitary fluid invading into the gap between the distal cover and distal structure. If the outer surface of the distal part should be in contact with an intracavitary wall, there would arise a possibility that the current flows to the intracavitary wall.